The present invention concerns a microwave dielectric ceramic composition and, more specifically, it relates to a microwave dielectric ceramic composition capable of reducing a temperature coefficient of a resonance frequency (hereinafter simply referred to as .tau.f) while maintaining non-load Q (hereinafter simply referred to as Qu) and, further, capable of optionally controlling .tau.f to positive and negative sides around zero as the center by controlling the mixing ratio of CaTiO.sub.3 or a specified oxide. The present invention also relates to a microwave dielectric ceramic composition and having high quality even if it is sintered at a low temperature due to the addition of a specified oxide or with less scattering in the quality even if it is sintered in a wide temperature range.
The present invention is applicable to impedance matching or the like of dielectric resonators, microwave integrated circuit boards and various kinds of microwave circuits in a microwave region.
Since the dielectric loss of a microwave dielectric ceramic composition (hereinafter simply referred to as a dielectric ceramic composition) tends to increase as the working frequency goes higher, a dielectric ceramic composition of high Qu in a microwave frequency region has been demanded.
As conventional dielectric ceramic materials, a dielectric ceramic composition of a crystal structure containing two phases, that is, a perovskite phase and an ilmenite phase (Japanese Patent Laid-Open Hei 2-129065) and a dielectric ceramic composition containing a predetermined amount of CaTiO.sub.3 in MgTiO.sub.3 and TiO.sub.2 (Japanese Patent Laid-Open Sho 52-118599) have been known.
However, the former dielectric ceramic composition obtained other ingredients such as Nd.sub.2 O.sub.3, La.sub.2 O.sub.3, PbO, ZnO in a great amount and, in addition, the value Qu is not always high. The latter dielectric ceramic composition contains TiO.sub.2 as the essential ingredient and .tau.f changes greatly as from +87 to -100 within a range for the mixing amount of CaTiO.sub.3 from 3 to 10% by weight to bring about a problem such as a difficulty for the control to a small value around zero.
The present invention intends to solve the foregoing problem and it is an object of the present invention to provide a dielectric ceramic composition capable of reducing .tau.f approximately to zero or optionally and stably controlling .tau.f to a desired value both to positive and negative sides around zero as the center while maintaining .epsilon..sub.r (relative dielectric constant) and Qu within practical characteristic ranges by controlling the addition (constitution) ratio of specified oxides (ZnO, Ta.sub.2 O.sub.5, Nb.sub.2 O.sub.5, MnO.sub.2, Al.sub.2 O.sub.3 or Co.sub.2 O.sub.3) and, further, having a high quality even if it is sintered at a low temperature or even if it is sintered in a wide temperature range due to the addition of a specified oxide.